Researchers develop modern tool
to measure heat stress in humans

The limits of human endurance, and the study thereof, are challenged by many factors: physical and mental fitness, terrain, heat, even the willingness of a test subject to provide a rectal thermometer reading in the field.

Athletes can exercise their bodies and prepare their minds, they can plot out the physical path of least resistance, but until recently, exercise physiologists struggled to ease the discomfort of taking accurate core temperatures while collecting data reliably.

UM Professor Brent Ruby and his fellow researchers at UM’s Montana Center for Work Physiology and Exercise Metabolism have turned their frustration at losing data into a simple, modern solution: an app.

Ruby has studied heat stress in wildland firefighters battling a blaze and ultramarathon runners racing more than 100 miles through Death Valley’s Badwater Basin. It’s no wonder it’s sometimes difficult to get these subjects to provide the gold-standard core temperature measurement.

"The instrumentation is pretty crude," Ruby says. "There’s the classic rectal thermometer, which is a piece of glass. The type of probes we use are flexible,
but they’re wired and have to be plugged into a data unit and battery charger or wall for power."

If it’s so difficult to gather, it’s a wonder researchers even bother with core temperature. But a person’s physiological strain index, the composite score of heart rate and a rectal temperature, provides vital information on how well a body is performing under heat stress, and if measured in time, can indicate the potential for sometimes deadly
heat injury.

In the mid-2000s, new body-temperature sensors were developed that a person could swallow like a pill. When the capsule reached the small intestines, core temperature data could be collected remotely without having to take a subject out of the field for an intrusive reading.

Ruby used these sensors as he began to gather data to develop and evaluate an equation, a predictive model that could capture overall physiological stress, as part of a U.S. Navy grant.

But as Ruby and other researchers soon discovered, the capsule sensors were prone to failure, sacrificing the integrity of data and time spent on a study.

"The devices didn’t work all the time," he says. "Breakdowns, failures. It’s expensive to use the equipment and lose the data 30 percent of the time."

To avoid that loss, UM researchers built off the equation they were developing to create a predictive model that could give the same information with easy-to-gather metrics.

Using Bluetooth sensors to measure heart rate and skin temperatures, the team now feeds data into a simple app, developed on the Android platform, to monitor a person during an activity.

Though the app originally was developed to help the team accurately capture their data, the ability to monitor heat stress live has changed the way researchers or even trainers and coaches can interact with the information.

While data gathered during an activity and later loaded into a system can tell a person that they did in fact surpass their comfortable core temperature just minutes before they collapsed, a live feed of the data can predict and prevent that heat injury.

"The app captures measures of the heart rate and temperatures, integrates those two and builds the heat stress score," Ruby says. "That number can be used to make decisions on whether you should slow down, get in the shade or tell you if you’re having issues."

Once the researchers realized the potential benefits of real-time monitoring, they got in touch with Joe Fanguy, UM director of technology transfer. Fanguy and MonTEC, the business incubator based at UM, help researchers and small businesses develop the entrepreneurial potential of their ideas.

Working with Fanguy, the team determined that the algorithm, not the hardware, is the piece of the project with commercial promise.

"Brent and his team are extremely creative and always coming up with new ideas," Fanguy says. "True to their creativity, this particular innovation is quite different, one where the commercialization strategy doesn’t necessarily involve patents for equipment or processes, but more along the lines of trade secrets."

The University currently is exploring product development options with a major sports equipment company, aiming to find a partner well-suited to design, manufacture and distribute a product based ultimately on Ruby’s research.

The app currently isn’t available on the Android or any other app market, since Ruby and his team just use it in their research, but the future of the tool is unknown. Ruby even sees potential in a multiuser live feed.

"It would be really cool to watch a football team of people who have been identified at risk of heat injury and monitor them to make sure they don’t get there," he says.

Although a rectal reading remains the most accurate measure of core temperature, the heat stress score displayed by the app can help people see a heat injury coming.

"Rectal temperature is too slow," Ruby says. "If you wait for someone to say, ‘Oh, I don’t feel good,’ it’s too late. If you could have intervened 30 minutes before, they wouldn’t have even gotten to that point."